1. Field of the Technology
The invention relates to multicast service macro diversity techniques, more particularly to a method, a system and apparatus for providing modulation and coding mode used by multicast service macro diversity.
2. Field of the Invention
With the rapid development of the Internet, a lot of multimedia services have emerged, some of which require the same data to reach multiple users at the same time, namely to be multicast, and such services may be video on demand, television on demand, video conference, online education, interactive games and so on.
3. Background of the Invention
Multicast is a technique that transfers data from one data source to multiple destinations, including multicast and broadcast. As to broadcast services, Cell Broadcast Service (CBS) in traditional mobile networks only allows transmitting low-bit-rate data to all users through the cell's shared broadcast channel, which belongs to message services. As to multicast services, there are IP multicast techniques in terms of the existing IP networks, but the mobile network has some characteristics different from those of IP network, such as network structure, function entities and wireless interfaces, so the current IP multicast techniques are not suitable for mobile networks. In addition, compared with common services, mobile multimedia services are of the characteristics such as large quantity of data, long time duration, delay sensitive and so on. Therefore, transmission using current techniques of broadcast services and multicast service are not suitable for data transmission of mobile multimedia services.
In order to effectively utilize wireless resources, the Third Generation Partnership Project (3GPP), which is a Wide Code Division Multiple Access/Global System for Mobile Communications (WCDMA/GSM) global standardization organization, provides Multimedia Broadcast/Multicast Service (MBMS), and on the other hand, Multicast and Broadcast Service (MBS) is introduced into the latest protocol IEEE802.16e/D5 of IEEE802.16. MBMS service and MBS service provide the specifications of multicast in the mobile networks, so that a mobile network can provide point to multipoint services, thereby network resources can be shared, utilization ratio of network resources, especially of the air interface, is increased. The newly provided MBMS and MBS service can realize multicast and broadcast of both low-bit-rate text messages and high-bit-rate multimedia services, and this is obviously the trend of future mobile traffic development.
The network structure of the MBS service in IEEE802.16 protocol is shown in FIG. 1. With reference to FIG. 1, a mobile network function entity, MBS server, is newly added to support MBS service, one function of MBS server is to act as entry of content providers, and another is to manage multicast data transmission of the Base Stations (BSs) belonging to the MBS server, as well as distribute multicast data to those BSs. In addition, function entities like Mobile Stations (MSs) and BSs need to be mended by adding MBS service-relevant functions.
The MBS service operation mainly includes following steps: obtaining MBS service list information, MBS service authentication and obtaining the key, and normally receiving the MBS service. Specifically, before normally receiving the MBS service, MS acquires information, such as MBS content list, from MBS server first, and then requests a BS to authenticate the received MBS service content; after successful authentication, the BS transmits MBS downlink service parameters and other information to the MS, the MS then requests the BS to return the MBS key. When receiving the downlink service parameters and MBS key, the MS can receive related Media Access Control Protocol Data Unit (MAC PDU) and begin to receive the MBS service normally.
As mentioned above, normally receiving MBS service mainly means receiving MBS service content with the received MBS downlink service parameters. In the current standard draft, MBS downlink service parameters mainly include MBS ZONE identifier and Multicast Connection ID (Multicast CID).
In order to support macro diversity, which can improve the receiving performance, MBS-MAP message is introduced into IEEE802.16e/D5, the latest edition of IEEE802.16, this message is transmitted in MBS ZONE and its Information Elements (IEs) are shown as table 1.
TABLE 1SyntaxSizeNotesMBS-MAP_Message_Format( ) { Management Message Type = ?8 bits Frame number24 bits The frame number is identical to the framenumber in the DL-MAP  for (I = 0; i < n; i++) {  Multicast CID12 bits 12 LSB of CID for multicast  Modulation and Coding mode4 bits(DIUC)  OFDMA Symbol offset8 bitsOFDMA symbol offset with respect to start ofthe MBS zone  Subchannel offset6 bits  Power Offset (Boosting)3 bits000: normal (not boosted); 001: +6 dB; 010:−6 dB; 011: +9 dB; 100: +3 dB; 101: −3 dB; 110:−9 dB; 111: −12 dB;  No. OFDMA Symbols7 bits  No. Subchannels6 bits  Repetition Coding Indication2 bits0b00 - No repetition coding0b01 - Repetition coding of 2 used0b10 - Repetition coding of 4 used0b11 - Repetition coding of 6 used  Next MBS frame offset8 bitsThe Next MBS frame offset value is lower 8 bitsof the frame number in which the BS shalltransmit the next MBS frame.  Next MBS OFDMA Symbol offset8 bitsThe offset of the OFDMA symbol in which thenext MBS zone starts, measured in OFDMAsymbols from the beginning of the downlinkframe in which the MBS-MAP is transmitted.   } If !(byte boundary) {  Padding Nibble4 bitsPadding to reach byte boundary. }}
The MBS-MAP message is used to notify each Multicast CID in the MBS ZONE of the physical channel resources allocated for them, including modulation and coding mode(s) of the burst, which is (are) indicated by a Downlink Interval Usage Code (DIUC), power offset, which is indicated by Boosting, and position of the next MBS frame. Therefore, if it correctly detects the MBS-MAP message, an MS can obtain the expected burst corresponding to the multicast connection, and the modulation and coding mode(s) used on the burst, and the power offset etc, then determines the position of the next MBS frame in this multicast connection, thereby normally receives the data through the multicast connection.
In the MBS-MAP message, the IE of DIUC is a 4-bit identifier used to identify the modulation and coding mode(s) used by current burst, and each form of the 4-bit identifier represents one kind of modulation and coding mode, thus the 4-bit identifier is also called a DIUC index, i.e., an index of modulation and coding modes. This DIUC value is defined in the Downlink Channel Description (DCD) message which is periodically broadcast by the current cell. Any change of the DCD message is identified by the Configuration Change Count in the DCD message and traced by using DCD count in other related information. For instance, DCD count is used in a Downlink Map (DL-MAP) message to track changes of the DCD message.
In the cellular systems, users at the edge of a cell endure poor communication qualities due to their long distance to the BS. To overcome this defect, macro diversity is introduced into cellular systems; with macro diversity, a receiver can receive signals from surrounding base stations, and extract useful signals from the received signals, thereby avoiding poor communication quality due to receiving signals from the single BS.
In the current solution, it is the current cell DIUC definition that the MBS service uses. To support macro diversity, all the cells in a MBS ZONE must utilize the same DIUC definition, which means sending the same DCD message. To realize that, an entity is needed to uniformly manage the DIUC definition of each cell, namely the definition of the DCD message.
Moreover, when receiving the MBS service, a receiver needs to continuously track the DL-MAP message in order to track the change of the DCD count, so as to determine whether to receive a new DCD message or not, in spite of the receiver is in SLEEP state or IDLE state, which is obviously a waste of power.